The Air Force says the launch was a success, but released no details of the mission's progress.

The service says the winged spacecraft will be a platform for unspecified experiments and can stay in orbit up to 270 days before gliding to an autonomous runway landing. The primary landing site is Vandenberg Air Force Base in California.

The X-37B began as a NASA project before being transferred to the Defence Advanced Research Projects Agency and then the secretive Air Force Rapid Capabilities Office.